From the bit of research I've done it seems that there isn't much information on this topic. I've read a number of keepers using garlic guard without issue but most seem to include it as more of a flavour enhancement. I imagine that at least should be safe.
The vitamins I think would likely depend on what exactly the contents of it are. I know with other amphibians like toads and salamanders they require calcium supplements I personally have a toad that I use a calcium supplement and reptivite with- while they aren't liquids I think they could potentially be used to make frog jello.